The present invention relates to aircraft control system. In particular, the invention relates to an actuation control system for components of an aircraft engine.
Aircraft require highly reliable control systems to ensure safe and efficient operation of the aircraft. Reliable control for more sophisticated gas turbine engines is maintained, for example, by a Full Authority Digital Engine Controller (FADEC). A FADEC receives cockpit commands in the form of a signal indicative of a performance level required from an engine. The FADEC also receives signals from a variety of sensors and other systems around the engine and the aircraft. The FADEC applies a set of control rules to the received signals and determines control signals to send to the engine.
Aircraft engines often include moveable components to adjust the operation of the engine. The moveable components are positioned by actuators. It is critical that the actuators position the moveable components accurately and, if not, that the failure of an actuator to position a moveable component accurately be detected and annunciated to a control or monitoring system, for example, a FADEC. An example of a moveable aircraft component is a variable area fan nozzle (VAFN) door. Moving a VAFN door changes the fan nozzle area to improve engine efficiency over a range of operating conditions. VAFN doors are typically employed in pairs, with one on either side of the aircraft engine. The VAFN doors must work together for effective control of the fan nozzle area.
Reliability requirements for aircraft actuation control systems are being driven to higher and higher levels in a continuous effort to improve aircraft safety. For example, requirements for VAFN control systems may permit no more than three control position failures per one million engine flight hours and no more than one unannunciated control position failure per ten billion engine flight hours. These stringent requirements necessitate robust, fault-tolerant designs for aircraft actuation control systems.